500
At the beginning of the movie, Ebeneezer Scrooge, a famous fictional character is very much like my next door neighbor.
What is incorrect?
The first phrase (at the beginning of the movie) is correctly followed by a comma because it comes before the clause (Ebeneezer Scrooge is very much like my next door neighbor. However this clause is interrupted by another phrase (a famous fictional character); phrases that interrupt clauses require a comma before and after the phrase. This sentence omits that should be after "character."